Machining tools of the generic type and especially end milling cutters for machining of fiber-reinforced materials (fiber composites) as carbon-fiber-reinforced plastic (CFRP), glass-fiber reinforced plastic (GFRP) or plastics reinforced with polyester threads have a plurality of main flutes circumferentially spacing a corresponding plurality of premachining lands and forming with each trailing premachining land a cutting wedge with a premachining cutting edge, and a plurality of auxiliary flutes corresponding to the plurality of main flutes, each auxiliary flute trailing a respective one of the main flutes, wherein each auxiliary flute circumferentially spaces a postmachining land of the premachining land leading in the circumferential direction and forms with the postmachining land a cutting wedge with a postmachining cutting edge.
This corresponds to finishing-roughing-cutters which are well-known from the metalworking and which are described, for example, in German Patent DE 3742942 C1, German utility model DE 8609688 U1 or U.S. Pat. No. 4,285,618 B, in which each roughing cutting edge is associated with a trailing finishing cutting edge.
In addition it is known from metalworking that to be able to accomplish in a single operation both the rough machining, i.e. a roughing work step, as well as the finish machining, i.e. a post-reaming or finishing work step, and thereby to come to a good surface quality within less processing time, in the milling and drilling of fiber-reinforced materials an additional problem should be resolved. A tearing out of individual fibers or a splicing of the thread is quite common when a workpiece from such a material is machined with conventional machining tools. Individual fibers are thus torn from the edge of the processing site, others are pressed during passage of the tool to the edge of the processing site, so that they are cut only on an end protruding over the edge of the machining point and therefore after processing protrude over the edge. By finishing, a cutting of the protruding fiber ends should be carried out, while at the same time a design of premachining cutting edges doing the main cutting work should be allowed, which is relatively blunt and doesn't tend much to a tearing out of individual fibers.
For example, German utility model DE 202 09 768 U shows a step drill for machining of sandwich materials, on which the main cutting edges at the step are offset to one another such that the one main cutting edge makes a pre-cutting and the other one a post-reaming. German utility model DE 202 11589 U1 shows another drill for machining sandwich material workpieces, wherein two premachining lands are more or less blunt designed as broaching tools and the postmachining lands trailing in the circumferential direction with sharp cutting edges as reaming tools. Similar drills are shown in the utility models DE 202 11592 U and DE 203 04580 U1, wherein broad circular grinding chamfers respectively grinding heels are used for reinforcement of the drilling hole and rounded cutting corners are used to prevent tearing of the thread.
At the tool shown in Japanese Document JP 2010-234462 A, left-hand twisted blades alternate with untwisted blades. European patent application EP 2554309 A1 shows a tool with on the one hand rectilinear cutting edges and on the other hand right-hand twisted cutting edges, which tool is intended for machining of materials such as carbon fiber reinforced plastic.
An end milling cutter for machining of fiber reinforced plastics is shown in German Patent DE 11 2009 000 013 B4, in which the idea of a separation of functions in main cutting work done by leading premachining lands and only post-processing work done by trailing postmachining lands has also been implemented. The leading premachining lands have a left-hand twist and the trailing postmachining lands have a right-hand twist to prevent burrs.